The tailormade ester functional epoxides, methyl 4,5epoxypentenoate (MEP) and t butyl 4,5-epoxypentenoate ( t BEP), were synthesized in good overall yields (60−65%) in short reaction sequences. Both MEP and t BEP were investigated as comonomers in the statistical copolymerization with ethylene oxide (EO) via the monomer-activated anionic ring-opening polymerization (MAROP), using triisobutyl-aluminum as a catalyst. Homopolymers and a series of copolymers of EO with varied molar contents of MEP and t BEP (0.6−31.3 mol %) were prepared, possessing molecular weights up to 11,800 g mol −1 . Surprisingly, in situ 1 H NMR kinetics studies revealed an ideally random copolymer microstructure for EO/MEP copolymers (r EO = 0.99, r MEP = 1.0) via MAROP for the first time. t BEP was found to be a less reactive comonomer, yielding gradient polyether structures (r EO = 2.9, r t BEP = 0.35). After polymerization, the ester-protecting groups were fully cleaved under basic or acidic conditions, respectively, resulting in either random or gradient distribution of carboxyl moieties. MTT assays demonstrated good biocompatibility of the novel carboxylic acid functional poly(ethylene glycol) (PEG) copolymers. The thermal properties of the copolymers were investigated via differential scanning calorimetry, showing the highly flexible nature of the PEG-based polyelectrolytes after deprotection. The liberated carboxylic acid groups were addressed with Ca 2+ cations, resulting in cross-linked polymer networks.
Dimethacrylate or divinyl-functionalized acetal-based crosslinkers were synthesized as building elements of acid-sensitive crosslinked hydrogels. Each crosslinker was prepared under catalytic acidic conditions with different functional groups installed at the acetal position. The hydrophilicity of the crosslinkers was tuned to control acidic-hydrolysis rate. We report the synthesis of hydroxyethyl dimethacrylatefunctionalized dimethyl ketal (CL1), meta-or para-methoxybenzaldehyde based acetals (CL2m and CL2p), poly(ethylene glycol) dimethacrylate-functionalized dimethyl ketal-based crosslinker (CL3), and divinyl-functionalized meta-methoxybenzaldehyde-based acetal crosslinker (V-CL2m). An examination of acetal hydrolysis kinetics of the monomers was performed in aqueous buffer solutions using 1 H NMR (proton nuclear magnetic resonance) and UV-Vis (ultraviolet-visible) spectroscopy at various pH ranges.The hydrolysis rates were strongly dependent on the structure of the acetal. Network films containing CL2m were prepared by thermally initiated polymerization with either hydroxyethylmethacrylate (HEMA) or methylmethacrylate (MMA). A study of the hydrolysis kinetics of these crosslinked films was performed using GC-MS (gas chromatography and mass spectroscopy) to understand the effect of monomer hydrophilicity, crosslinking density, and polymerization mechanism at different pHs. The crosslinked films composed of the hydrophilic monomer, HEMA, show faster hydrolysis than those containing more hydrophobic monomers (e.g. MMA). The hydrolysis rate decreases as the crosslinking density increases. In the case of thiol-ene networks formed by reacting pentaerythritol tetrakis(3mercaptopropionate) and V-CL2m, each repeating unit is composed of an acid-degradable acetal-moiety.Hydrolysis of the thio-ene network films results in depolymerization into two lower molecular weight components, pentaerythritol tetrakis(3-(6-hydroxyhexylthio)propanoate) and meta-methoxybenzaldehyde.
The ring opening polymerization of cyclic carbonates made from epoxide and CO2 to CO2-containing polymers constitutes an emerging technology of particular industrial interest. Considering the reaction of ring-opening polymerization of...
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